1. Field of the Invention
The present invention relates to a noise-reducing, highly absorbent and water-permeable concrete, known as drainage concrete, a process for its production, and its use as, for example, open-pored road surfacing.
2. Description of Related Art
In recent years, the environmental consciousness of people has risen considerably, also with regard to noise pollution. Owing to the great rise in traffic density, particularly on highways, the subject of traffic noise now occupies a central position.
The causes of traffic noise are:
drive of the vehicle (drive noise/engine noise), PA1 rolling of the tires of the road surface (tire-road noise/rolling noise). PA1 a) radial tire vibration: PA1 b) resonance of the air between tire and road surface: PA1 c) adhesion: PA1 d) collision of profile elements: PA1 The noise is reduced at the source, i.e. the motor vehicle or the motor vehicle tires. PA1 The area over which the noise spreads is limited by protective walls and protective embankments. PA1 the megatexture (texture wavelength 50-250 mm), PA1 the macrotexture (texture wavelength 1-50 mm), PA1 the acoustic impedance (sound absorption). PA1 the porosity (accessible void content), PA1 the flow resistance (permeability), PA1 the structure factor (pore structure in the accessible voids, connection of the pores to one another), PA1 the thickness of the layer.
The rolling noise is caused mainly by the following:
impact of the profile elements on the road surface, PA2 compression of the tire profile as a result of the surface texture, PA2 pipe resonance, PA2 Helmholz resonance, PA2 air pumping, PA2 tangential vibration as a result of stick-slip movements, PA2 tearing off of profile elements, PA2 water film and acceleration of water droplets (only in the case of a wet road surface).
Lawmakers have taken account of the increased occurrence of noise with "(German) Guidelines for noise abatement on roads--1990 edition--RLS--90" and "16th (German) Regulations for implementation of the Federal Law on Environmental Protection" (Traffic Noise Regulations--16th BImScH V). To achieve these aims, the following measures are still mainly applied:
Recently, efforts have also been made to reduce the spread of noise from the road surfacing. The largest influences on the sound emission of a road surface are
On driving over a porous road surface, the air under the vehicle tires can escape into the voids of the road surfacing, so that, in particular the high-frequency region of the rolling noise is reduced. The absorption should be as effective as possible in the frequency range of human hearing and indeed preferably in the particularly sensitive region between about 200 and 2000 Hz.
The acoustic impedance of an open-pored road surface is determined by:
In practice, highly porous surfacings have proven useful as surface layer, for example drainage asphalt or "whisper asphalt". Open-pored or highly porous road surfacings allow the sound level to be reduced by up to 5 dB(A) in comparison with traditional dense surfacings. However, for open-pored asphalt surfacings the currently expected life is at most 6 years, so that such open-pored surfacings have to be replaced substantially more often than conventional dense asphalt surfacings.
Compared with asphalt, concrete basically has the advantage of a considerably longer life, so that concrete surfaces require less frequent maintenance work. Efforts are therefore being made to furnish concrete surfacings with appropriate noise-reducing properties (Intron Report No. 94 229, Porous Concrete--Laboratory tests, pages 11-12). At the same time, however, the positive properties of the concrete, for example high durability, should be retained.
Modifying concrete with polymers to improve the application properties is basically known. According to DE-A 42 12 325, concrete modified with styrene/acrylate dispersion gives water-impermeable articles. However, for sufficient water permeability and high sound absorption, the porosity and the structure factor of the concrete should be as high as possible.
In the attempts made hitherto to produce polymer-modified porous concretes, it was found that void content and strength display opposite trends. The higher the void content, the lower the strength of the road surfacing. At the same time, in the case of a void content which is acoustically effective, the strength was found to be insufficient for highly stressed road surfacing. In the experiments carried out hitherto, the bonding between the acoustically effective road surfacing and the concrete underneath was also found to be insufficiently durable (Intron Report No. 94 229, Porous Concrete--Laboratory tests, page 73).